Certain polarized electrical components, such as tantalum capacitors, diodes and other PN junction devices are normally constructed so as to have a single positive terminal located at one end of the component and a single negative terminal located at the other end of the component. This choice of terminal designation is determined by the internal polarity of the material within the component proper. When the positive and negative terminals of the electrical component are connected respectively to the energized positive and negative leads on a printed circuit board, the polarized component becomes electrically charged in the desired or forward direction. However, when the polarized component becomes charged in the incorrect or reverse direction, component breakdown, shorting, circuit failure, fire or all of the above will sometimes occur within a certain time after the component has been energized. Thus, there is a requirement that these polarized electrical components be placed at the correct orientation within the plane of the electrical circuit board receiving the polarized components. This problem has been previously discussed in the prior art such as, for example, in Parson's U.S. Pat. No. 4,027,207 assigned to IBM and incorporated herein by reference.
A rapidly growing technology in which this correct orientation and biasing of small electronic components is required is that known as surface-mount technology (SMT). Using this technology, both electrical components and conductive traces for making connections thereto are installed on the same side of a substrate surface. For a further discussion of some of the fundamentals of this technology, reference may be made to an article by F. M. Mims, III entitled "Introduction to Surface Mount Technology", RadioElectronics, November 1987, pp 59-70 or to U.S. Pat. No. 4,722,470 assigned to IBM. Both of these publications are also incorporated herein by reference.
Once the above components have been mounted in a particular orientation on a printed circuit board, or as part of a surface-mounted device, or both, they are electrically tested to see if they are forward biased in the correct forward polarized direction. This testing requirement adds time and expense to the printed circuit board assembly process, and in the specific case of polarized tantalum capacitors, electrical testing is usually ineffective in identifying an incorrect reversed polarity condition. That is, component breakdown and failure do not usually occur until a certain time has elapsed after reverse bias is improperly applied thereto.